Processing well fluids



Feb. 22, 1944.

w. B. PLUMMER I 2,342,165-

PROCESSING WELL FLUIDS 3 Sheets-Sheet 1 Filed Dec. 20, 1939 Feb. 22, 1944. w. B. PLUMMER 293429165 PROCESSING WELL FLUIDS Filed Dec. 20. 1939 3 Sheets-Sheet. 2

F w. B. PLUMMER 2,342,1465

PROCESSING WELL FLUIDS Filed Dec. 20, 1939 3 Sheets-Sheet 3 PRODUCT INPUT will J'AACTIbNA FJPRER WE LL atented Feb. 22, 1944 rnooassmo WELL FLUIDS William B. Plummer, Chicago, 111., assignor to Standard Oil Company, Chicago, 111., a combration of Indiana Application December 20, 1939, Serial No. 310,200

1 Claim.

line hydrocarbons and hydrocarbons boiling somewhat above the gasoline range as well. The existence of these hydrocarbons in the vapor phase in the sub-surface reservoir is due to the high pressure existing in the formation which brings about a phenomenon known as retrograde vaporization whereby a hydrocarbon system which would give a liquid phase as well as a vapor phase at moderate pressures or even at atmospheric pressure exists as a single dense vapor phase in the reservoir. In handling production from such reservoirs the well fluids are reduced in pressure and sometimes cooled to bring about the phenomenon of retrograde condensation whereby a large part of the normally liquid hydrocarbons and also a substantial part of the three and four carbon atom hydrocarbons .are thrown out in the liquid phase and separated. This liquid phase is-then stabilized or flashed to atmosphereic pressure and the gases originally separated as well as those resulting from the stabilization or flashing operation are recycled to the underground formation from which they were produced thereby maintaining the pressure in such formation and maintaining or enhancing the retrograde vaporization phenomenon therein, thus greatly improving the ultimate recovery from the reservoir. In some instances these gases are used for the maintenance of the pressure in, or the repressuring of, an underground formation other than that from which they originated.

It has also been proposed to recover the liquid components of high pressure well fluids, of the type described, by processes of high pressure abgasoline is present in the gas) and to wells producing a liquid phase as well as a gas phase at the well head.

It is an object of the present invention to provide methods for enhancing the yield of motor fuel in connection with production from oil and gas wells and particularly in conjunction with production from wells of the distillate type. An-

other object of the invention is to accomplish this increased production of motor fuel without seriously diminishing the amount of gas available for recycling to the sub-surface reservoir or for cycling to another sub-surface reservoir. A still further object of the inventionls to provide a method for increasing the yield of motor fuel in conjunction with producing operations of the type previously mentioned while simultaneously increasing the amount of gas available for recycling purposes.

Another object of my invention is to provide in the connection previously described a gas of improved character for pressure maintenance or repressuring purposes.

It is also an object of the invention to accomplish the foregoing objects with simple apparatus having a dual function. A further object of my invention is to accomplish the objects previously described in 'a particularly economic and ex- A further object of my invention is to provide a new and improved absorption medium for use in high pressure absorption processes in connection with production from wells of the distillate pe.

Other and more detailed objects, advantages and uses of my invention will become apparent as the description thereof proceeds.

The normal production from distillate wells includes a large amount of methane and progressively lower amounts of higher parafflnic hydrocarbons. Ordinarily this includes a substantial amount of C2. C3 and C4 hydrocarbons, a substantial amount of hydrocarbons boiling in the gasoline range, i. e., up to about 400 F., and usually a fair and varying amount of still heavier hydrocarbons. It is customary in conjunction with both the retrograde condensation and the high pressure absorption types of process for handling such production to recycle practically all of the hydrocarbons having one, two and three carbon atoms per molecule and a large part of the four carbon atom hydrocarbons to the underduction of methane in the polymerization operaground formation. In spite of this the amount of gas available for recycling purposesis necessarily quite considerably less than that produced so that pressure maintenance is not ordinarily completely successful. This is due first to the fact that the desirable normally liquid hydrocarbons are recovered and are not available for' recycling and also to the fact that the fuel necessary in whatever prooessis used and in particular the fuel necessary for the operation of compressors is normally taken from the gas produced and this further diminishes the supply of recycle gas. Any process for the 'utilization of any of the normally gaseous hydrocarbpns produced by such distillate wells has therefore been looked at askance-since it is still further and more seriously diminishes the supply of recycle material. However, the process of my invention utilizes certain of. these lower hydrocarbons for the production of further amounts of hydrocarbons boiling in the motor fuel range without seriously diminishing the supply of gases tion is accompanied by the production of cyclic hydrocarbons. notably benzene and other aromatic hydrocarbons which are highly desirable in a motor fuel. At the same time heavier aromatic hydrocarbons boiling above the gasoline boiling range are produced and these are highly useful in a high pressure absorption operation since the high critical temperature of aromatic hydrocarbons permits the operation of the absorption step at a higher' pressure than would otherwise be the case. Since any increase in the pressure of the high pressure absorption operation diminishes the most expensive step of the process; namely, that of recompressing the gases for recycling to the sub-surface reservoir, the improved utility of this high pressure absorption medium is apparent. Thus not only does the polymerization operation produce large volumes of hydrogen and methane which are highly useful for recycling purposes, but without diminishing the supply of gas available for recycling an improved motor fuel is obtained in greater yields than would otherwise be the case and an improved high pressureabsorp- 2Q tion medium is simultaneously produced.

While the preferred embodiment of my invention involves the production of well fluids, particularly from reservoirs of the distillate type, the recovery of a normally liquid fraction, the separate recovery of a fraction 01' normally gaseous available for recycling and in many instances it serves to increase the supply of such gases as well as improving their function in the underground retrograde vaporization phenomenon.

Briefly this is accomplished by the isolation of a fraction heavier; than methane and lighter than gasoline, normally a CaC4' fraction, subjecting this at high temperatures and preferably at high pressures to a thermal polymerization process which produces not only a large amount of gasoline range hydrocarbons but alsoiian amount of gas of even greater volume than the gaseous volume of the hydrocarbons going to the polymerization operation. These gases are available for recycling and thus avoid the objection previously described. The thermal polymerization process involves amongst other reactions the dehydrogenation of C: and C4 hydrocarbons and of ethane to some extent and the polymerization of the olefinio hydrocarbons thus produced to form normally liquid hydrocarbons which ordinarily boil largely in the gasoline range but include a heavy polymer fraction which is very useful in connection with a high pressure absorption operation.

If the dehydrogenation and polymerization reactions were the only ones involved, one molecule of hydrogen would be formed for each molecule of hydrocarbon consumed in the process. Thus the amount of gas available for recycle would not be diminished. Also the hydrogen is believed to have a substantially greater retrograde vaporization effect than do the hydrocarbons from which it was formed. However, the process is even more advantageous than this since other reactions are involved producing hydrocarbons lighter than those consumed. In par-ticular these thermal polymerization processes are notable for the production of a very substantial amount of methane which is excellent for recycle purposes. In fact the substitution of methane for a heavier hydrocarbon such as propane or butane makes the gas,

volume per volume, much more eflicient in the retrograde vaporization phenomenon. This prohydrocarbons heavier than methane, the thermal polymerization of this latter fraction and the recycling of all or part of the gases produced in the thermal polymerization operation along with those directly separated from the well fluids to the underground formation or to another under ground formation, my invention also includes subjecting a fraction of normally gaseous hydrocarr bons heavier than methane to separate steps of 40 dehydrogenation and polymerization, both of which steps may be catalytic and may be accomplished at various temperatures and pressures by the use of various catalytic processes known to the art. These catalytic processes commonly operate at low pressures.

My invention :will be described further with particular reference to'the accompanying-draw- 'ings which show in Figures 1, 2 and3 respectively three alternative flow diagrams illustrating my invention. These drawings form a part of this specification and in them like reference numerals indicate like or corresponding parts.

Turning first to Figure 1, a producing well. I I Y furnishes well fluids from a sub-surface reservoir which is normally a deep high pressure reservoir of the distillate type. While only a single prov ducing well is shown it will, of course, be ap parent that the production from any number of" such producing wells can be combined and that normally my process will operate on the combined production from a group of such producing wells. The well fluids pass through valve II (which may be fully open) and then through line ii to one or the other of driers l4. These driers may contain any desired drying material, for instance f calcium chloride. The particular drier used at any particular time is, of course, controlled by the operation of valves l5. Normally one drier is on stream and the other is being regenerated by passing hot gases therethrough by the use of valves I6. The purpose of the drying operation is to remove water which would otherwise form natural gas hydrates on reduction of the temperature and pressure, thereby interfering with the operation of the subsequent apparatus. However, ifthe temperature and pressure of the separation step are such that with the particular well -fluid involved hydrate formation does not occur to a troublesome extent, the drying step can. of course, be omitted.

The well fluids, preferably dried, pass through cooler l1 and pressure reduction valve l8 to separator IS. The cooler and pressure reduction valve are controlled to give a temperature and pressure in the separator which may be varied within considerable limits depending on the desired operation and the particular character of the well fluids. However, they are such as to give a substantial recovery of liquid hydrocarbons by virtue of the retrograde condensation phenomenon. Normally the pressure in separator l9 will be between 600 pounds per square inch and 2,000 pounds per square inch and is a chosen on an economic basis. In other words, the pressure should be as high as possible in order to reduce the cost of. recompressingthe gases but, on the other hand, the lower the pressure so long as it remains within the retrograde condensation range, the larger the amount of liquid phase separated. The lower limit of the retrograde condensation range varies with the composition of the particular well fluids'involved and is in general higher when these well fluids are rich in heavy hydrocarbons than when they are poor in heavy hydrocarbons. In most cases the pressure in separator 19 should be between 900 pounds per square inch and 1,800 pounds perfsquareinch, the higher'pressures generally corresponding to well fluids rich in heavy components and the lower pressures to well fluids poor in such heavy components.

Generally speaking, the lowerthe temperature in separator IS, the better the recovery and here again we have 'an economic factor involving thecost'of cooling and 'thecost of eliminating hydrate ditficulties. The separator can be operated mally gaseous hydrocarbons, particularly. C1 and C4 paraflinic hydrocarbons; y Theygas'fphase in thisseparator is predominantlymetha'ne but also inc amounts-of heavier p p ssors land thence through n Ila 1316,13. to oneor more input wells which 'it'isrecycled. to the underround formation from which production was effected through well II or it may be cycled to a the liquid phase from separator l9 along with all or part of the hydrocarbons produced by the polymerization step are separated in it into a liquid phase which is withdrawn through valve 30 under the control of float 3| and then through cooler 32 to product storage tank 33 and a gaseous phase which is withdrawn from the top of the fractionator through line 34. The liquid product in tank 33 contains the gasoline pro duced by both the retrograde condensation step and the polymerization step. It will also normally contain some small amount of heavier hydrocarbons and in many instances some slight excess of light hydrocarbons so that re-running and often stabilization are necessary in order to produce a finished motor fuel. Due to the presence of the polymer gasoline, such a finished fuel is of high antiknock value and high quality although further refining operations can be and often will be applied to it.

The gases withdrawn from the top of fractionator 29 through line 34 include practically all the propane and lighter hydrocarbons present in the liquid phase from separator I9 as well as in the initial product from the polymerization step and also include a substantial part,

often amajor part, of the C4 hydrocarbons produced in the two operations. This gas stream passes to separator 35 in which a liquid phase rich in C3 and C4 hydrocarbons is separated by virtue of the operation of partial condenser 36. These liquid hydrocarbons are removed from the separator by pump 3] and a portion of them may be and normally is recycled as reflux to fractionator 29' by means of valve 38 and line 39. Since the hydrocarbons recycled to the fractionator largely return to separator 35, the liquid phase from this separator is ultimately cycled via valve 40, line 4|, heat exchanger 42 and line 43 to polymerization furnace 44 for conversion into normally liquid hydrocarbons. particularly gasoline range hydrocarbons.

It will be understood that depending on the pressure and top temperature in fractionator 29 be largely C4 hydrocarbons or largely propane whichever isdesired. Normally the predominant different sub-surface reservoir for pressure maintenance or repressuring purposes. As previously pointed out, these gases act on the sub-surface reservoir to improve the ultimate recovery therefrom.

Turning now to the liquid phase in separator I I9, this is removed through valve under the control of float 26 and passes vi-a line 21 and one or the other of valves 28 into fractionator 29. This fractionator is preferably a bubble and on the amount of cooling efiectuated by cooler 36, the liquid phase in separator may hydrocarbon is propane. It will also be apparent that if the pressure in fractionator 29 is high and the top temperature of this fractionator is low the bulk of, the C4 hydrocarbons along with a large part of the propane can be eliminated from fractionator 29 into product tank 33 instead of going to separator 35. In this case, which is normally not the preferred operation, the product in tank 33 will, of course, require stabilization and the liquid phase in separator 35 will be rich in ethane. polymerizer M are rich in at least one normally gaseous paraflinic hydrocarbon heavier than methane.

Turning to the gas phase in separator 35 this is removed via line 45 and passes through valve 45 to compressors 41 by means of which its pressure is increased to about the same pressure as that of the off-gases from separator l9 and the gases from separator 35 then pass along with those from separator 19 to compressors 2| for reinjection through input well or wells 24,

'When the conditions are such that the gases from separator 35 contain substantial amounts of polymerlzable hydrocarbons, a portion of these gases can be sent to polymerizer 44 via one of Thus the. hydrocarbons going to compressors 41, valve 48, lines 49 and 4|, heat exchanger 42 and line 43.

It is also normally desirable to use a portion of the gases from separator for fuel in polymerization furnace '44 and these can be taken through valve 50, lines 5| and 52 and valve 53 to burner 54. Gas tank 55 is floated on the line or can be used to accumulate a portion of the gases produced. The amount of gas thus used as fuel is much less than that produced in the polymerization step, the remainder being available for use underground for pressure maintenance or repressuring purposes.

Adverting now to polymerizer 44 in more detall, the hydrocarbons entering it are preheated by means of heat exchanges 42, if so desired, and then pass with any desired routing through the coils of the polymerization furnace. This polymerizer is preferably operated at a temperature of 950 to 1150" F., for instance 1025 F., and at a pressure of 100 to 3000 pounds per square inch, for instance 1500 pounds per square inch. It is preferred to operate the polymerizer at a high pressure, preferably at least 1,000 pounds per square inch, to minimize recompression costs. As previously indicated, other types of polymerization systems can be used, preferably high temperature thermal polymerization systems but also including thermal and catalytic systems in which the gases are first dehydrogenated and then polymerized in a separate operation. While the operation of the polymerization step involves dehydrogenation as well as polymerization, in the strict sense of the latterterm, I refer to the combined reactions, whether occurring together or in separate steps as polymerization. This is in accordance with usage in the art.

As shown the initial product from the polymerizer 44 passes out through transfer line 56 and then through heat exchanger 42 where it serves to preheat the incoming gases. The polymerization products then pass to evaporator 51' from which a heavy polymer fraction boiling above the gasoline range is removed via valved line 58 which is under the control of float 59.

r The vapor phase material from evaporator 51 passes through line 60 into fractionator 29.

Since the polymerization products entering fractionator 29 are normally at a much higher temperature than that of the liquid phase from separator l9, the polymerization products are introduced into the fractionator at a low level and the liquids from the retrograde condensation step enter at a high level. Thus the latter serve to supply a dephlegmating or reflux effect and greatly reduce or even eliminate the necessity of supplying other reflux or dephlegmation to the fractionator. On the other hand, the hot polymerization products serve to supply at least a large part and usually all of the heat required at the bottom of this fractionator and eliminate or greatly reduce the amount of reboiler heat which must otherwise be supplied at the base of this fractionator. In other words, the fractionator 29 is not only used to accomplish a double function in connection with the fractionation of the retrograde condensation products and the polymerization products as well but the two streams are utilized in such manner as to make for a peculiarly eflicient'fractionation operation.

While the simple flow diagram and apparatus arrangement shown in Figure 1 is particularly advantageous in many respects, it is also advantageous in other instances to use more complicated flow diagrams. This is particularly true where large production is available and where the character of the formation and production from it are such that the productivity of the producing well or wells declines only very slowly so that a high capital investment is justifiable to obtain increased efiiciency. Figure 2 illustrates some of these possibilities and also illustrates a simple process alternative to that of Figure 1 utilizing only a portion of the apparatus shown in Figure 2.

Adverting now to Figure 2 in more detail the production from one or more producing wells II which are preferably of the distillate type passes through cooler I1 and pressure reduction valve l9 into vessel l9 which, if valves GI and 62 are closed and no absorber oil is introduced, operates as a retrograde condensation separator similar to that shown in Figure 1. One difference, however, is that instead of drying the gases entering separator 19 as in Figure 1, Figure 2 shows the use of an antifreeze system as an alternative method of preventing natural gas hydrate trouble. A liquid or gaseous antifreeze material, for instance calcium chloride brine, can be circulated with the well fluids through pressure reduction valve l6 and this serves to prevent the formation of natural gas hydrates. In the case of a liquid antifreeze material this, ,of course, separates at the bottom of separator l9 and is withdrawn under the control of float 63, which floats at the interface between the brine and the hydrocarbons, through valve 64 to an antifreeze, regeneration, storage and recycling system 65 from which it goes back into the line either preceding or following cooler I7. As shown the regenerated antifreeze is returned via valved line 66 between cooler I1 and pressure reduction valve l8.

As in the case of Figure l, the gases, chiefly methane, from separator l9 pass through line 20 and compressors 2| which are shown as controlled by the pressure in line 20 and thence through line 22 to one or more input wells 24.

Turning to the liquid hydrocarbons in separator 19, these are withdrawn through valve 25 under the control of float 26 and pass, by means of line 21, to surge drum 61. This surge drum can be operated at about the same pressure as separator I9 in which case it serves only as a surge drum or it may be operated at a pressure intermediate between that of separator 19 and that of stabilizer 29 in which case it serves not only as a surge drum but also as a separator. Thus, for instance, the retrograde condensation separator l9 can be operated at 1,200 pounds per square inch, the surge drum and separator l9 at 600 pounds per square inch and the stabilizer 29 at 300 pounds per square inch.

The liquid present in surge drum 6! passes through pressure reduction valve 68 into stabilizer 29. Before entering the stabilizer, all or part of it can be used, if so desired, to cool the stabilized product by wholly or partially closing valve 69 and opening valves 10, thereby passing this cooled stream from the surge drum through heat exchanger 1 I. On the other hand, it is often advantageous to utilize the low temperature'of this material from the surge drum not as an indirect heat exchange material in heat exchanger H but rather a refluxing material. When the stream from the surge drum has not been passed through heat exchanger 1| prior to introduction into the stabilizer, the point of introduction is.

preferably the one corresponding to the upper of the three alternative valved lines 12.

In stabilizer 29 hydrocarbons lighter than off-gases from the stabilizer through partial condenser 35 to separator 35 from which a part of the liquid phase can be pumped by means of pump 31 through valve 38 and line 39 back into the top of stabilizer 29. If the hot material from polymerizer .44 is introduced into stabilmer 29 through valve 13, as will hereinafter be discussed, little or no reboiling will be necessary.

However, if this is not the case, i. e., if a separate fractionation apparatus is used for the polymerization products, reboiling can befurnished by means of trap-out plate I4 and heater I5. In fact some heating at this point may be desirable even if the hot polymerization products are discharged into the stabilizer.

Stabilized material from stabilizer 29 is cooled in heat exchanger II and/or cooler 32 and then passes to intermediate product storage tank 33. Since the material in this intermediate product storage tank normally contains a considerable amount of hydrocarbons boiling above the gasoline range, it may be rerun and is therefore withdrawn by means of pump 16 and passed through line TI to rerun tower I8. When rerunning is carried on immediately cooler 32 may be bypassed by closing valve 32a and opening valve 32b.

Rerun tower I8 can be operated at low pressure and is aconventional piece of equipment. If cooler 32 has been used the material from intermediate product tank 33 can be used to cool the hot bottoms from rerun tower I8 by closing valves I9 and opening valves 80 thus passing this can be withdrawn through valved line 88 for shipment, chemical treatment or use. On the other hand, it can be passed through valved line 09 and line 90 and blended in line 9I with the gasoline produced in the polymerization operation and this is in general desirable since the polymer gasoline has a relatively high knock rating and the distillate gasoline has a relatively high volatility so that the two together make an excellent motor fuel.

The bottoms from the rerunnlng operation are cooled in heat exchanger 8I and/or cooler 92 and thence passed through valved line 93 to storage tank 94. Alternatively part of this heavy distillate can be passed through valved line 95 to tank 96 and blended with the heavy polymer which, as will hereinafter appear, is normally the main product passing to this tank. As a matter of fact, heavy distillate tank 94 can be dispensed with and all of this heavy distillate can be passed along with the heavy polymer to storage tank 96. However, this is not preferred particularly when vessel I9 is operated as a high pressure absorber rather than as a mere retrograde condensation separator since the heavy polymer is a better absorption medium than is the heavy distillate.

Returning now' to separator 35 in connection with stabilizer 29, the liquids from this sepa- 5 rator are ultimately pmsed by pump.3l through valve 40, line M and heat exchangers 42 into the coils of polymerization furnace 44.

The gases from separator 35, on the other hand, can be utilized in a variety of ways which will depend for the most part upon their composition. This in turn depends on the pressures chosen for various parts of the apparatus and on the composition of the original well fluids. If gases from surgedrum 61 are not used as fuel, gases from separator 35 can be used as part or all of the fuel for polymerizer 44 in which case the necessary portion of these gases is passed through valve 91, line 98 and valve 53 to burner 54 of polymerizer 44. 'Fuel gas storage tank normally floats on the line. On the other hand. the gases from separator 35 ordinarily contain some substantial amount of polymerizable constituents and it is therefore desirable to pass all or part of them through valve 99, compressors I00, valve IOI, lines 49 and 4|, heat exchangers 42 and line'43 to the coils of polymerization furnace 44. The third possibility which is desirable when fuel gases are available from other sources and when, as is ordinarily the case, the gases from separator 35 do not contain large amounts of polymerizable hydrocarbons is to pass all or part of these gases through valve 99, com- Pressors I00, valve I02, compressors I03, line I04, line 20, compressors 2|, and line 22 to input well 24. I prefer, particularly when polymerizer 44 discharges into stabilizer 29, to cycle the greater part of the gasfrom separator 35 to the input well or wells. I

Turning back now to polymerizer 44, this can be operated under the conditions described in connection with Figure 1 and the hot materials from the polymerization coils can be cooled in heat exchangers 42 and then passed into stabl lizer 29 through valve 13. This has the advantages discussed in connection with Figure 1 of using a. single column for two purposes and utilizing the hot stream from the polymerizer and the cold stream from the distillate recovery operation to good advantage in eliminating or cutting down the amount of reflux and reboiling necessary in connection with this tower. When this operation is carried out in this fashion, tanks 33, 01 and 94 will, of course, contain the polymer product as well as the distillate product and stabilizer I05, fractionator I06, bubble tower I01 and tanks '96 and I08 together with associated equipment, can be eliminated.

On the other hand, it is sometimes advantaeous to keep the polymerization products entirely separate from those of the distillate recovery operation and when this is. desired valve 13 sibility is to utilize a separate fractionation-system only for such part of the polymer products as it is desired to keep separate and to retain the advantages of single tower operation insofar as the bulk of the polymer products is concerned. This can, of course, be accomplished by the control of valves 13 and I09.

The material, if any, from valve I09 passes through line H0 and is used if so desired to heat reboiler III whereupon it enters fractionating column I06 which is operated in such fashion that a portion of the gasoline is taken overhead and a portion is eliminated in the bottoms. Fractionator I06 can be supplied with dephlegmator [I2 and reboiling apparatus H3. The overhead from this fractionator'passes into stabilizer I through I and one of the three alternative valved lines H5. The bottoms from this stabilizer are withdrawn through valve I I 6 and passed through cooler -I II to polymer storage tank I08 as part of the stabilized polymer gasoline product. The overhead from this stabilizer passes through line H8 and partial condenser II9 to separator I20. A portion of the liquid phase from this separator may be passed by pump I2I through valve line I22 to serve as reflux in stabilizer I05 and the remainder is recycled through valve I23, line I24, line 4I, heat exchangers", and line 43 to the coils of polymerization furnace 44 to produce higher ultimate yields of polymer gasoline. The gas phase from separator I20, on the other hand, may be handled in any one or more of the three alternative ways discussed in connection with the gas phasefrom separator 35. Thus it may be passed through valve I25, compressors I26, valve I21, line 49, etc., to the coils of polymerizer 4.4; or through valve I28 and line I29 to burner 54 or to gas storage tank 55; and/or it may be passed through valve I25, compressors I26, valve I30, compressors I03, line I04, line 20, compressors 2|, and line 22 to one or more input wells 24-. This latter is the preferred operation since it is highly desirable to keep up the amount of gas available for recycling to the formation and this gas, being rich in hydrogen, is a particularly desirable material for recycling. In many instances it will be possible to eliminate part of the compressors referred to since it will not be desired to utilize all of the possible alternative arrangements shown.

Reverting now to the bottoms from fractionating column I06, these can be used if desired to cool the bottoms from bubble tower I01 by closing valve I3I and opening valves I32, thus passing this hot stream through heat exchanger I33 and thence through line I34 into the bubble vtower. This bubble tower is conventionally equipped with dephlegmating means I35 and reboiling means I36. It is so operated as to eliminate a heavier than gasoline bottoms and a gasoline overhead. The latter is passed through conde'nser I31 and line I38 to polymer product tank I08, while the bottoms pass through heat exchanger I33 and cooler I39 to heavy polymer tank 96.

The polymer product of gasoline boiling range can be withdrawn from tank I08 through valved line I40 for storage, further treatment or use or can be and preferably is withdrawn through valve I 4| and line I42 for admixture with the distillate gasoline in line 9|.

Similarly the heavy polymer can be withdrawn from tank 96 for any desired purpose through valved line I 43 and the heavy distillate from tank 94 can similarly be withdrawn through valv'ed line I44. However, it is advantageous to use one or both of these materials as an absorber oil and absorber oil, the heavy distillate is withdrawn through valved line I44, valve I45 being closed, while such part of the heavy polymer as is needed for absorption oil passes through valve I46, pump I41, line I48 and one or both of valves 6| and 62 into the absorber I9.

Vessel I9 when operated as an absorber can usually be operated at a somewhat higher pressure and, if desired, at a slightly higher temperature than when operated as a retrograde condensation separator. Thus as an absorber its pressure may range from 1,000 to 4,000 pounds per square inch, usually from 1,200 to 3,000 pounds per square inch, for instance 2,000 pounds per square inch. The absorber oil in any desired ratie, for instance two to six gallons per thousand cubic feet of gas, can be introduced above bailies I50 or part of it or even all of it can be passed through cooler I1 into the absorber along with the well fluids. The absorber oil, of course, is removed from vessel I9 along with the distillate hydrocarbons and finds its ay through surge drum 61 and stabilizer 29 to7intermediate storage tank 33 and ultimately to heavy distillate storage tank 94. By going through this route it becomes contaminated, of course, with the heavy distillate and in the preferr d operation newly produced heavy polymer is cgntinuously sent to the absorber as absorption medium since its aromatic character and high c itical temperature make it possible to operate abs rber I 9 at a higher pressure than would otherwise be the case. This reduces the amount or compression necessary for recycling the gas to the underground formation or for cycling it to another underground formation and makes for a great reduction in capital costs as well as operating costs.

Figure 3 shows an alternative type of flow diagram combining high pressure absorption and polymerization. A,

In this figure the products from producing well Il may be passed through one of drilers I4 and thence through cooler II and pressure reduction valve I8, all as described in connection; with Figure 1. It will be understood, however, that some of these apparatus elements may be omitted depending on the character of the well fluids and the character of the subsequent operations. Thus,

. for instance, if the well fluids are available at erated as a high pressure absorber.

to operate vessel I9 as a high pressure absorber I rather than merely as a retrograde condensation separator since recovery of distillate can, ordinarily be increased quite substantially by so doing.

As has been mentioned previously, the preferred absorber oil is the heavy polymer and this is one of the principal reasons for using a separate fractioning system on at least a part of the polymer products. In connection with small installations it will be apparent that this fractionating system can be considerably simplified. In the preferred operation using heavy polymer as moderate pressure, for instance 1,500 or 2,000 pounds per square inch, pressure reduction will not ordinarily be needed and is not desirable. If the product is very low in water content or if the absorber is operated at a temperature above that at which hydrates form under the particular pressure conditions involved, the drying step can likewise be omitted. However this may be, the

well fluids enter a high pressure absorber I9 which may be operated under the temperature and pressure conditions referred to in connection with vessel I9 -of Figure 2 when the vessel is'op As in the case of Figure 1, gases from the top of absorber I9 pass through line 20, compressors-"2| and line 22 into one or more input wells 24. The distillate along with the absorber oil, the introduction of which will be described hereinafter, passes out of absorber I9 through valve 25 which is under the control of float 26 and thence passes through line 21 and pressure reduction valve I5I to gas separator I52. The gases flashed off in this separator pass through line I53, valve I54 and one of compressors I55 and thence through heat exchangers I56, 42a and 42b into the coils of polymerizer 44. A portion of these gases mayalso be used as fuel passing through valves I51 and 53 to burner 54 with fuel gas tank 55 floating on the line.

The question of which gases will be used for fuel, which for charge to the polymerization fur- 4 and particularly C3 and C4 hydrocarbons, to the polymerization step to improve the ultimate yield of motor fuel. Ideally the gas used as fuel should be low pressure gas poor in polymerizable constituents, i. e. methane and hydrogen, but it is not possible to make a perfect balance between these various factors particularly since the gases available at the highest pressures are usually those which are poorest in polymerizable constituents.

Liquids from separator I52 are removed from the bottom thereof through valve I58 under the control of float I59 and passed through line I60 to a second gas separator I6I, thus giving a stage flashing operation. For example, absorber I9 can be operated at 2,000 pounds per square inch, gas separator I52 at 1,000 pounds per square inch and the second gas separator I6I at 500 pounds per square inch. Gases from this second separator pass out through valve I62, lines I63 and I64 and compressors I55 through heat exchangers I56, 42a and 42b into the coils of polymerization furnace 44. Since these gases are richer in polymerizable constituents than those from gas separator I52, it is not desirable to use any of the gases from the second separator as fuel. The liquid phase from this second separator passes out through valve I65 under the control of float I66 to surge drum I61 from which gases may be taken off through valve I66 and line I69 and passed along with those from separator I6I throughlines I63 and I64, compressor I55, etc., to

polymerizer 44,

The liquid from this surge drum is drawn of! through pressure reduction valve I10 and may be used to cool the bottoms from stripper IN by closing valve I12 and opening valves I13, thus sending the cool stream through heat exchanger I14 and increasing its temperature prior to entry stituents are taken overhead while the heavier than gasoline constituents can be removed through valve I15 (valves I16 and I11 being closed) and thence through heat exchanger I14,

.pump I16, heat exchangers I56, cooler I19, line I80 and valves I8I to absorbers I9 and I82. Part of this heavier than gasoline fraction must be removed through valved line I63 if valves I16 and I11 are closed.

Returning now to polymerizer 44, the initial polymerization products pass out through trans fer line 56, heat exchangers 42b and 42a, line I64, heat exchanger I65, which serves as a reboiler for stripper Ill and thence through line I66 and optionally through heat exchanger I81 under the control of valves I68 into absorber I82. This absorber normally operates at a pressure substantially under that in absorber I9. The gas from absorber I82 passes out through valve I99 and compressors I03 into line 20 from which it is sent toone or more sub-surface formations. Also thegas from the top of absorber I62 may be used as fuel. being introduced by means of valve I and line I9I. Liquid is withdrawn from the bottom of absorber I62 through valve I92 which is under the control of float I93. It may then pass through valve I94 and its pressure may be boosted by means of pump I95, thus making it possible to introduce it into gas separator I52 which normally operates at a somewhat higher pressure than absorber I82. For instance, this absorber may operate at 800 pounds per square inch and gas separator I52 at 1,000 pounds per square inch as previously mentioned. On the other hand, absorber I82 may be operated at a considerably higher pressure, for instance 1,000 or 1,500 pounds per square inch and pump I95; can therefore sometimes be omitted. Alternatively, therefore, these liquids can be introduced by means of valve I96, line I91,

valved line I08 and line I60 into gas separator I6I or through valved line I99 into surge drum I61 depending on the pressures involved.

Whatever route is chosen, at least the hi her boiling fraction of the polymerization products together with the absorber oil from absorber I82 join the distillate and absorber oil from absorber I 9 in surge drum I61 and pass with it into stripper I II as previously described.

The overhead from stripper I1I passes through partial condenser 200 to separator 20I from which gases can be taken off through valve 202, line 203, line I63, compressors I55, etc., for introduction into the polymerizer. The liquids from this separator are withdrawn by means of pump 204 and a portion of them is returned to the top of the stripper through valve 205 and line 206 to serve as reflux. The remainder passes through valve 201 and line 208 and thence in whole or part, if so desired, through heat exchanger 209 under the control of valves 2 I0 and then through line 2 and one or both of valved lines 2| 2 into stabilizer I05 which is equipped with reboiler III. In this stabilizer the combined distillate and polymerization products are reduced to the desired flash point and the motor fuel product is withdrawn through valve I I 6, heat exchanger 209 and cooler I I1 to storage tank 2I3.

Gases from stripper I05, rich in butanes, are taken off through line I I8 and partial condenser I I9 to separator I20, the liquid phase being sent in part through pump I2I and valve I22 to the top of the stabilizer as reflux and in part through valve I23 and line I24. This latter part joins in line I24 with the gaseous phase from the top of separator I20'which is withdrawn through valve I25 by compressors I26 and then passed through a coil 2I4 in absorber I82 in order to cool the latter and heat the material going to the polymerization coil. This material then passes through heat exchangers I81 and 42b into the coils of polymerizer 44 from which its course is that previously described.

Reverting to stripper HI, I have described sending the entire heavier than gasoline fraction through valve I15, heat exchanger I14, pump I18, etc., for use as-absorber oil and, in part, for discharge from the system. However, it is often desirable to use instead of the entire heavier than'gasoline fraction, a particular cut from the heavier than gasoline fraction. This can be done by closing valve I15 and opening valves I16 and Ill. The heavier than gasoline fraction then passes through valve H6 and line 2! 5 into fractionator 2 l6 equipped with dephlegmating coil 2 and and reboiler 2l8. This fractionator can be used to produce various cuts such as an overhead cut withdrawn through valve 219 and/or valve 22'), side stream cuts withdrawn through any one or more of valves 22! and a bottom out withdrawn through valve 222 and/or valve 223. Any of these four cuts can be discarded from the system through header 224 and any one of them or any combination of them can be used as absorber oil via header 225 and/or line 226, valve I", heatexchanger I", pump I18, heat exchangers I56, cooler I19, line I80 and valves I8! leading to absorbers l9 and I82.

Similarly, of course, fractionation of the ma.- terial to be used as absorber oil could be applied to the flow diagram of Figure 2 in which the polymerization products and distillate products are kept separate. Thus, for instance, the polymerizer bottoms or heavy polymer in tank 96 of Figure 2 could be fractionated as described in connection with Figure 3 and the desired fraction could be sent to absorber l9.

lt'will be understood, of course, that the variousflow diagrams presented are merely illustrative of some of the possibilities and that other alternatives will occur to those skilled in the art in the light of this description and that my invention is not restricted to the details shown. on the other hand, it will also be understood that these flow diagrams are simplified for purposes or convenience and that various items of pumping and compressing equipment, insulation, control devices, safety equipment and various other details are not indicated.

Having described my invention what I desire to claim is: j

A method of recovering distillate hydrocarbons from high pressure well fluids and for the manufacture of additional amounts of motor fuel hydrocarbons from said well fluids which comprises fractionating said well fluids at an elevated pressure and a low temperature into a predominantly gas fraction and a liquid fraction containing substantial amounts of both normally gaseous hydrocarbons and gasoline range hydrocarbons, introducing said liquid fraction into a vertically elongated Lractional distillation zone at a high level therein, removing from said fractional distillation zone at least one fraction rich in gasoline range hydrocarbons and at least one fraction rich in polymerizable normally gaseous hydrocarbons, subjecting at least a major amount of said last-mentioned fraction to a high temperature at an elevated pressure to cause thermal polymerization, and passing at least a major amount of the hot polymerization products into said fractional distillation zone at a low level therein.

WILLIAM B. PLUMMER. 

